The present invention is directed to a dental patient chair having an adjustable headrest that is pivotably hinged to a bracing member around a first transverse axis and the bracing member is adjustable in a longitudinal direction of the backrest, the headrest is pivotably connected to a link at an offset second axis, so that the first transverse axis forms a lever arm together with the second axis and an application of either tensile or compressive forces by an adjustment arrangement to the link causes a pivoting of the headrest.
Taking ergonomic perceptions into consideration, a design of a dental treatment chair occurs in view of adapting the motion sequence of the headrest of the dental treatment chair to the natural nodding motion that the head of a patient situated in the dental treatment chair executes when the head is brought into various treatment positions. This is particularly difficult to implement for the two extreme positions, namely the extreme "extension position" on the one hand, wherein the head and, thus, the headrest should be highly inclined in a backward direction in comparison to the backrest for an upper jaw treatment to give a direct view into the patient and, on the other hand, for the "prothetic position", wherein the head should be inclined forward to such an extent given an upright backrest position until, for instance, a horizontal occlusion plane is reached.
U.S. Pat. No. 4,515,406 discloses a design wherein a bracing carrying the head support is fashioned as a circularly curved, narrow plate that contains the center of a circle that lies approximately in the cervical vertebra joint of a patient sitting in the chair. The curved plate is guided in a slot held adjustably along the backrest and can be moved into and out of the carriage or, respectively, the backrest on the basis of a hydraulic drive.
Even though this design proves physiologically beneficial and allows a relatively narrow thin headrest shape, this arrangement has some disadvantages. Due to the brace member's guidance, the motion angle of the headrest is highly restricted. In addition, a relatively bulky mechanism is required in the upper backrest part. Given this design, every attempt to design the backrest thinner in this region, which would be inherently desirable in order to position the patient's head as low as possible in the fully reclining position, but to, nonetheless, have adequate freedom for the knees of the attending person, would lead to a further restriction of the kinematics in this design and, thus, the positioning possibilities for the patient's head. An additional disadvantage may be seen wherein the adaptation to relatively tall patients is only conditionally possible and extremely tall patients are lent no support in the neck region in this particular arrangement.
Another headrest which, also, is only adjustable within limits is disclosed in German OS 36 11 282. In this particular design, the two extreme positions recited at the outset can be only inadequately set. By contrast to the above-mentioned design wherein the headrest itself can be executed relatively flat and thin, the headrest in this particular design is constructed relatively thick because of the tilt mechanism provided therein, and this is disturbing in view of the optimally great freedom of legs or, respectively, knees that the attending person desires when the backrest is greatly inclined. An adaptation of the size of the patient is also only conditionally possible in this known design. Extremely tall patients, likewise, have no adequate support for the neck region.
U.S. Pat. No. 4,840,429, whose disclosure is incorporated herein by reference thereto and which claims priority from German Application 37 27 204, discloses another headrest design wherein the parallelogram-like linkage is hinged to the backrest or, respectively, to a carrier part held in the backrest. The pairs of articulations of this linkage form a four-bar mechanism having articulation spacings of different sizes. Whereas the pair of articulations having the smallest articulation space is arranged approximate to the backrest, the pair of articulations provided with the largest articulation spacing is arranged distal of the backrest. The pair of articulations distal from the backrest is formed by an articulated connection of the two articulated arms with the movable part of a straight-line mechanism provided in the longitudinal direction of the headrest. The one linkage arm is provided with a roller lever that is supported against a guideway which is rigidly secured in the housing of the headrest. The movable part is moved relative to the fixed part of the straight-line mechanism with a drive motor. Even though the two extreme positions mentioned in the beginning can be achieved rather well with this adjustment mechanism, the mechanism provided in the head support here has a relatively thick wall structure.